Why Do Dogs, Cats, Camels, and Llamas Make That Weird Face?

Please stop what you’re doing—which, presumably, is reading this article—and do a quick Google image search. You don’t even have to type anything—just click here. (I promise, there’s nothing unsavory at the other end, but its phasers are set to giggle.)

Ladies and gentlemen, what you’re seeing is the flehmen response, a scent-sucking mechanism employed by many mammalian species, and I’d argue the best dang animal-related search on the Internet.

But the flehmen response is au natural. The goats and tigers and tapirs you see here have not been provoked in any way. They do not have peanut butter on the roofs of their mouths, nor have they been trained to respond to a cue. They’re just animals doing animal stuff—and looking like a gang of proper goofs while doing it.

So, what the actual flehmen is going on here?

Also known as the lip-curl, the gape response, or more simply, funny cat face, the flehmen response is a behavior some animals use to investigate a smell. You can witness flehmening in everything from the house cat on your lap to rhinos, rams, elk, llamas, and giraffes.

What the actual flehmen is going on here?

Courtesy of Yathin Krishnappa

John Bradshaw, an anthrozoologist and author of myriad books about animals, says it’s easy to mistake the behavior for aggression, since the animal bares its teeth as it scrunches up its face. But what’s actually happening is that the cat or moose is physically opening up two tiny ducts on the roof of its mouth behind its incisors.

“If you’ve got an older dog—supposing it’s a friendly animal—you can pry its face apart and look up and see them,” says Bradshaw. “The ducts are a couple of millimeters wide, and in their normal state they look like little, flat slits.”

Officially called the nasopalatine canals, these ducts go up through the roof of the mouth and connect with something called the vomeronasal organ (aka the Jacobson’s organ). Bradshaw explains that this is a sort of accessory olfactory bulb, with completely different neurons than the ones associated with the sense of smell.

In fact, scientists think that the information processed by this organ lies somewhere in between the sense of smell and taste. The ducts are full of saliva, so whatever molecules get trapped in there have to be physically pumped up to the vomeronasal organ with special muscles. Whereas an animal can’t help but automatically take in smells when it breathes through its nose, the flehmen response is a voluntary action, like swallowing.

So, why do buffaloes and hedgehogs require a spare form of sniffing? And aren’t dogs already supposed to have some of the most superpowered schnozzes in the biz?

Interestingly, Bradshaw says that cats may have the better end of the deal when it comes to vomeronasal organs. The average tabby has 30 different types of receptors up in there while your hound dog has just 9.

“Presumably, if you’ve got three times as many receptors, you can discriminate between a lot more things,” says Bradshaw.

In other words, when a cat goes into full flehmen, it isn’t just sniffing. It’s sniffing in high resolution.

But if we really want to talk about super sniffers, we need to look at the meek. In Bradshaw’s book Cat Sense, he writes that mice have hundreds of receptor types. “The odorants mice pick up regulate reproduction, as well as enabling recognition of every other mouse in the neighborhood from its unique odor ‘fingerprint.’ ”

Most animals, and this is true for cats especially, seem to use their flehmen response when investigating smells from other members of their own species. This means the vomeronasal organ is important for mating, marking territory, and intraspecific communication.

But this isn’t a hard and fast rule. One study conducted with Saanen goats found that the animals used the flehmen response to investigate urine from 15 different mammal species, three bird species, and two reptile species. In the trial, the goats seemed to flehmen more intensely in contact with the urine of farm animals than with that of zoo animals. But who knows, perhaps goats just flehmen anytime they get sprayed in the face with urine. (I’d probably make a funny face, too.)

By the way, not all animals that have vomeronasal organs perform the flehmen response. Elephants do a pseudo-version of the behavior, but supplement it by physically bringing smells into contact with their ducts, which are on the top of their mouth cavities. So if you ever see an elephant at the zoo touching a puddle of urine with its trunk and then putting that same yucky trunk into its mouth—it’s not eating the urine, it’s flehmening it. Similarly, snakes have no need to snarl. They transfer scent molecules directly to the organ using their forked tongues, which fit into those tiny mouth pits like a plug into a socket.

If your tongue has been searching the roof of your mouth for holes, fear not. Humans lack these special ducts and the vomeronasal organs to go with them. In fact, that’s probably why you’ve never heard of the flehmen response—it’s not something we can do.

But this probably wasn’t always the case—our ancestors certainly flehmened, and you can see evidence of it during development. When the human fetus forms, it actually sets out on a path toward building a vomerosonal organ.

“But then at some point it just fades away and disappears,” says Bradshaw.

When the baby is born, the only remaining clues are a pair of pits at the bottom of our nostrils where the ducts used to connect to the organ—a nonfunctional token of our evolutionary past.